The chief purpose of the Clinical Core is to establish and maintain an acute hepatitis C virus (HCV) tissue repository. Better understanding of spontaneous recovery of HCV infection is necessary to improve methods to prevent and treat chronic infection. A major limitation is the rare recognition of acute infection in humans. We have overcome this obstacle by following persons at risk for HCV infection monthly. By screening for HCV infection and careful monitoring of acutely infected persons, we have established an acute infection repository that has already been used by immunologists to advance our understanding of acute hepatitis C. In this competing renewal, the clinical activities are focused in a Clinical Core whose aims are to recruit and monitor HCV antibody negative young injection drug users, to clinically characterize acute infection when it occurs, and to establish and maintain an acute infection repository and distribute the resources to NIH funded investigators. By accomplishing these aims, the Clinical Core will make a major contribution to our understanding of hepatitis C recovery and achieve many of the objectives of RFA-AI-04-028.